大象传媒

Transformers

In an electrical circuit, energy is transferred each second. This is electrical . The power output of a transformer can be calculated using the equation:

power = potential difference 脳 current

This is when:

  • power is measured in watts (W)
  • potential difference is measured in volts (V)
  • current is measured in amperes, also referred to as amps (A)

Assuming that a is 100 per cent efficient, the following equation can be used to calculate the power output from the transformer:

potential difference across primary coil 脳 current in primary coil = potential difference across secondary coil 脳 current in secondary coil

Example

A step-down transformer converts 11,500 V into 230 V. The power output is used to run a 2,000 W kettle. Calculate the current in the primary coil (the input current).

(The power in each coil will be the same, since transformers are 100 per cent efficient.)

\(power = 2,000~W\)

Rearrange the formula to find current:

\(Current~in~primary~coil = \frac{power}{potential~difference~in~primary~coil}\)

\(Current~in~primary~coil = \frac{2,000}{11,500}\)

\(Current = 0.174~A\)

The National Grid

When electricity is transmitted around the country on the , the transmission wires get hot and energy is to the surroundings.

Step-up transformers at a power station increase the voltage which reduces the current. The smaller the current, the less energy is dissipated so stepping-up the voltage makes the transmission of electricity more efficient.